全文获取类型
收费全文 | 11329篇 |
免费 | 1138篇 |
国内免费 | 3篇 |
专业分类
12470篇 |
出版年
2023年 | 48篇 |
2022年 | 112篇 |
2021年 | 228篇 |
2020年 | 99篇 |
2019年 | 152篇 |
2018年 | 187篇 |
2017年 | 171篇 |
2016年 | 312篇 |
2015年 | 477篇 |
2014年 | 522篇 |
2013年 | 615篇 |
2012年 | 886篇 |
2011年 | 883篇 |
2010年 | 564篇 |
2009年 | 516篇 |
2008年 | 727篇 |
2007年 | 704篇 |
2006年 | 623篇 |
2005年 | 652篇 |
2004年 | 659篇 |
2003年 | 589篇 |
2002年 | 597篇 |
2001年 | 137篇 |
2000年 | 111篇 |
1999年 | 128篇 |
1998年 | 144篇 |
1997年 | 99篇 |
1996年 | 100篇 |
1995年 | 92篇 |
1994年 | 82篇 |
1993年 | 90篇 |
1992年 | 63篇 |
1991年 | 69篇 |
1990年 | 78篇 |
1989年 | 84篇 |
1988年 | 68篇 |
1987年 | 51篇 |
1986年 | 49篇 |
1985年 | 47篇 |
1984年 | 51篇 |
1983年 | 61篇 |
1982年 | 57篇 |
1981年 | 50篇 |
1980年 | 50篇 |
1979年 | 30篇 |
1978年 | 37篇 |
1977年 | 36篇 |
1975年 | 24篇 |
1973年 | 28篇 |
1971年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
Gregory Plunkett Donald F. Senear Glen Zuroske Clarence A. Ryan 《Archives of biochemistry and biophysics》1982,219(2):463-464
Proteinase inhibitors I and II were purified to electrophoretic homogeneity from leaves of tomato plants induced by either wounding intact plants or by supplying excised plants with the proteinase inhibitor inducing factor. Affinity chromatography with chymotrypsin-Sepharose was employed as a final purification step for each inhibitor. The tomato leaf inhibitors are very similar to potato tuber inhibitors I and II in subunit molecular weight, composition, and inhibitory activities against chymotrypsin, trypsin, and subtilisin. However, unlike the potato tuber which contains multiple isoinhibitors by isoelectric focusing, the tomato leaf exhibits only two isoinhibitor forms of inhibitor I and a single form of inhibitor II. The molecular weight of native potato inhibitor I was reevaluated by rigorous ultracentrifugal analysis and compared with data from previous analyses. The data confirm that native inhibitor I has a native Mr of about 41,000 and is a pentamer. Inhibitor II has a molecular weight of near 23,000 and is a dimer. 相似文献
23.
24.
25.
Concentrations of soluble aluminum (Al) and manganese (Mn) frequently reach phytotoxic levels in acid soils. While dose response relationships for these metals are well documented, the effects of combined exposure have received less attention. We have examined the effect of combinations of Al and Mn on growth and metal accumulation in Vigna unguiculata (L.) Walp. grown in solution culture under conditions of low ionic strength (conductivities typically < 100 µS cm−1 ). The nature of interaction between these metals varied with the specific physiological response, the part of the plant investigated, and the relative amount of stress imposed. Analysis of growth data provided evidence for amelioration of metal toxicity (antagonistic effects), although this effect was dose dependent. Analysis of metal content data provided evidence for antagonistic and synergistic (exacerbation of toxicity) effects, again depending on dose. Analysis of foliar symptoms also provided evidence for antagonisms and synergisms, with the nature of the response dependent on the specific physiological response and specific plant part investigated. In contrast with previous reports, evidence for antagonistic, synergistic, and multiplicative effects on growth, metal uptake, and expression of foliar symptoms have been obtained under physiologically and environmentally relevant conditions. These results suggest a more detailed analysis of the potential for interactions between metals in the environment is required. 相似文献
26.
Jake V Bailey Verena Salman Gregory W Rouse Heide N Schulz-Vogt Lisa A Levin Victoria J Orphan 《The ISME journal》2011,5(12):1926-1935
We present evidence for a dimorphic life cycle in the vacuolate sulfide-oxidizing bacteria that appears to involve the attachment of a spherical Thiomargarita-like cell to the exteriors of invertebrate integuments and other benthic substrates at methane seeps. The attached cell elongates to produce a stalk-like form before budding off spherical daughter cells resembling free-living Thiomargarita that are abundant in surrounding sulfidic seep sediments. The relationship between the attached parent cell and free-living daughter cell is reminiscent of the dimorphic life modes of the prosthecate Alphaproteobacteria, but on a grand scale, with individual elongate cells reaching nearly a millimeter in length. Abundant growth of attached Thiomargarita-like bacteria on the integuments of gastropods and other seep fauna provides not only a novel ecological niche for these giant bacteria, but also for animals that may benefit from epibiont colonization. 相似文献
27.
Gregory Charles Westergaard 《International journal of primatology》1995,15(6):899-906
Via Oswalt’s system of classification, I compare the tool-kits of wild and captive capuchins with those of Tanzanian chimpanzees and Tasmanian aborigines. The results indicate that capuchins have tool-kits that are smaller, and have lower ratios of artifacts to naturefacts, than those of Tanzanian chimpanzees and Tasmanian aborigines. Accordingly, Oswalt’s system can be used productively to assess the relative technological skills of monkeys versus those of apes and humans. 相似文献
28.
Rachel M. Haywood Andrew W. D. Claxson Geoffrey E. Hawkes David P. Richardson Declan P. Naughton Gregory Coumbarides Jane Hawkes Edward J. Lynch Martin C. Grootveld 《Free radical research》1995,22(5):441-482
High field (400 and 600 MHz) proton NMR spectroscopy has been employed to investigate the thermally-induced autoxidation of glycerol-bound polyunsaturated fatty acids present in intact culinary frying oils and fats. Heating of these materials at 180°C for periods of 30, 60 and 90 min. generated a variety of peroxidation products, notably aldehydes (alkanals, trans-2-alkenals and alka-2, 4-dienals) and their conjugated hydroperoxydiene precursors. Since such aldehydes appear to be absorbed into the systemic circulation from the gut in vivo, the toxicological significance of their production during standard frying practices is discussed. 相似文献
29.
Tristan J. Iseli Nigel Turner Xiao-Yi Zeng Gregory J. Cooney Edward W. Kraegen Sheng Yao Yang Ye David E. James Ji-Ming Ye 《PloS one》2013,8(4)
We recently showed that bitter melon-derived triterpenoids (BMTs) activate AMPK and increase GLUT4 translocation to the plasma membrane in vitro, and improve glucose disposal in insulin resistant models in vivo. Here we interrogated the mechanism by which these novel compounds activate AMPK, a leading anti-diabetic drug target. BMTs did not activate AMPK directly in an allosteric manner as AMP or the Abbott compound (A-769662) does, nor did they activate AMPK by inhibiting cellular respiration like many commonly used anti-diabetic medications. BMTs increased AMPK activity in both L6 myotubes and LKB1-deficient HeLa cells by 20–35%. Incubation with the CaMKKβ inhibitor, STO-609, completely attenuated this effect suggesting a key role for CaMKKβ in this activation. Incubation of L6 myotubes with the calcium chelator EGTA-AM did not alter this activation suggesting that the BMT-dependent activation was Ca2+-independent. We therefore propose that CaMKKβ is a key upstream kinase for BMT-induced activation of AMPK. 相似文献
30.